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Ann. Geophys., 20, 771-779, 2002
www.ann-geophys.net/20/771/2002/
© European Geosciences Union 2002
Strong sunward propagating flow bursts in the night sector during quiet solar wind conditions: SuperDARN and satellite observations
C. Senior1, J.-C. Cerisier1, F. Rich2, M. Lester3, and G. K. Parks4
1Centre d’Etude des Environnements Terrestre et Planétaires (CETP), 4 Avenue de Neptune, 94107 Saint-Maur Cedex, France
2AFRL, Hanscom Air Force Base, MA 01731, USA
3Radio and Space Plasma Physics, Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
4Space Sciences Laboratory, University of California Berkeley, Berkeley, CA 94720–7450, USA
Correspondence to: J.-C. Cerisier
(jean-claude.cerisier@cetp.ipsl.fr)
Abstract. High-time resolution data
from the two Iceland SuperDARN HF radars show very strong nightside convection
activity during a prolonged period of low geomagnetic activity and northward
interplanetary magnetic field (IMF). Flows bursts with velocities ranging from
0.8 to 1.7 km/s are observed to propagate in the sunward direction with phase
velocities up to 1.5 km/s. These bursts occur over several hours of MLT in the
20:00–01:00 MLT sector, in the evening-side sunward convection. Data from a
simultaneous DMSP pass and POLAR UVI images show a very contracted polar cap
and extended regions of auroral particle precipitation from the magnetospheric
boundaries. A DMSP pass over the Iceland-West field-of-view while one of these
sporadic bursts of enhanced flow is observed, indicates that the flow bursts
appear within the plasma sheet and at its outward edge, which excludes Kelvin-Helmholtz
instabilities at the magnetopause boundary as the generation mechanism. In the
nightside region, the precipitation is more spot-like and the convection
organizes itself as clockwise U-shaped structures. We interpret these flow
bursts as the convective transport following plasma injection events from the
tail into the night-side ionosphere. We show that during this period, where the
IMF clock angle is around 70°, the dayside magnetosphere is not completely
closed.
Key words. Ionosphere (Auroral ionosphere; Ionospheremagnetosphere
interactions; Particle precipitation)
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